Whether this heralds a new arms race isn't certain though. For starters, the US and Russia are already in a race to develop new weapons, particularly in cyber and the unmanned sphere.

The US claims a new Russian ground-launched cruise missile, the Novator 9M729, violates the landmark 1987 arms control pact banning nuclear and conventional missiles with ranges of 310 miles to 3,420 miles.

The US does, but Mr Trump has lost his majority in the House and it's unlikely Congress would approve increased spending on what is already a vast nuclear arsenal. His ambitions might be thwarted at home.

China is a factor: although a nuclear state, it isn't bound by the terms of the INF.

That undoubtedly rankles with Mr Trump, who tends to believe most international treaties are weighted against the US (Paris Climate Accord, Trans Pacific Partnership, Iranian Nuclear Deal).